Bio-control of prevalent Ralstonia solanacearum strains in major tomato growing areas using Mykovam and BioGroe, land determination of their modes of action

Bacterial wilt caused by Ralstonia solanacearum is the most serious disease of solanaceous vegetables such as tomato, potato, eggplant, bell pepper, as well as more than 200 plant species including banana. Farmers experience 15 to 50% losses both in the lowlands and in the mountain slopes. Disease management has been difficult because of broad host range, vast genetic viability, wide distribution and absence of resistant cultivars. The project hopes to help in the control and management of bacterial wilt disease through the use of mycorrhizal fungi available as 'Mycovam' and plant growth-promoting bacteria(PGPR) available as 'BioGroe'. Results of several post rials showed that the application of biofertilizers can potentially suppress or diminish the effect of R. solanacearum strains on the tomato host plant. However, the success of the biocontrol capabilities of the biofertilizers may depend on the following factors: 1) timing of application, the earlier the biofertilizers applied the better, and 2) R. solanacearum strain prevalent in the site, where some strains are more virulent than the others. The project also showed the potenial biocontrol capabilities in vitro of new microbial isolates against specific strains of R. solanacearum. Results of virulence assays confirmed the differential virulence of several strains, whereby other R. solanacearum strains are capable of causing higher degree of wilting on tomato hosts, specifically R. solanacearum strain T463 and T625 which was more virulent than other strains like Tm7 and Tm22. In terms of multiple biocontrol agents, there was no significant difference in terms of biocontrol action between single and multiple strain formulations. Biofertilizer inoculation in the seed/seedling stage improved growth of tomato plants compared to the control as shown in the taller height, and greener leaves. Observations showed that the bigger plants had greater resistance to or were less susceptible to the wilt pathogen as compared to the smaller/shorter not inoculated tomato plants. Furthermore, biofertilizer inoculated seedlings had lesser number of plants wilted at the end of the 16 days observation period compared to the control. These results indicate that biofertilizer application in tomato seedlings can potentially decrease the rate of bacterial wilt pathogen infection and minimize crop mortality. However, the right biofertilizer(microbial strain) must first be identified and applied as early as possible to the tomato seedlings so that they can establish in the roots before the infection of the bacterial wilt pathogen. Further research is needed to verify growth inhibition of new microbial isolates.